The present invention relates to a pH sensitive electrode that has an electrochemically inactive and electrically insulating or semi-conductor core coated with a thin coating of electrochemically active electrode material, and supported in an elastomeric body that has an opening to leave a portion of the sensitive coating exposed to a chemical sample. A conductor carries the signal generated at the chemical coating interface to suitable circuitry and the entire electrode assembly can be mounted in an outer housing to form a pH sensor. Preferably the core is made of alumina and the coating is deposited iridium oxide.
In the prior art, various pH sensors have been advanced, using an electrochemically active material which may be in the form of a solid bar, a cap, a sleeve or the like, or which may be a metal-metal oxide type electrode where the active material is a coating on an electrically conductive substrate. Some electrochemical active coatings have been applied to flat insulating substrates, but the signal connections are difficult to make because the connections have to be made on the active face and then insulated and sealed to protect the connections from the sample gas or solution with a chemical resistant epoxy or other material.
Most prior art electrodes are adhesively bonded to an assembly body, and most adhesives either deteriorate with age or are very fragile. Minute leakage of the sample solution that is being tested to the back of the electrode and/or its electrical connection is not unusual and the leakage results in a loss of signal or the generation of an extraneous electrochemical signal. Many of the problems of sealing the coated core and maintaining a sealed conductor coating interface are solved with the present invention.